Composite elastic yarns, including an inner elastic yarn, such as e.g. a single filament yarn, of so-called Lycra®, elastan or other polyurethane fibers or the other, are frequently used in the production of fabrics and particularly knitwear, such as, for example, hosiery. The elastic yarn is covered by a less elastic yarn, which may be considered essentially not elastic, such as, for example nylon®, or other polyamide, polyester or equivalent, typically with a multiple filament structure, i.e. a yarn made of a plurality of strands. This yarn will hereof be called “covering yarn” because it is used to form a sort of coating or covering of the elastic yarn.
The covering of the elastic yarn may be obtained by means of a spiraling process in which the elastic yarn is covered with a helical winding of covering yarn. This process is extremely costly and slow.
A new process of covering or coating elastic yarn has been recently affirmed. This process—known as “interlacing” or “air covering”—consists in using a pneumatic device, commonly called an interlacing jet with a conduit crossed by two yarns (the covering yarn and the elastic yarn). A pressurized air nozzle lets a jet of compressed air into the conduit. The turbulence generating inside the conduit interlaces the covering yarn around the elastic yarn. Devices and methods based on this technology are described in U.S. Pat. No. 6,393,817, U.S. Pat. No. 5,008,992, U.S. Pat. No. 4,829,757, U.S. Pat. No. 3,940,917.
This technology employs pneumatic systems originally developed for machining multiple filament threads to increase bulk and entangle the individual filaments forming the yarn. Examples of interlacing jets developed for this application and used to interlace elastic or elastomeric yarns with covering or coating yarns are described in U.S. Pat. No. 5,970,593, U.S. Pat. No. 5,146,660, U.S. Pat. No. 5,010,631, U.S. Pat. No. 4,430,780, EP-B-564400, JP-A-3,279,437.
The spools of elastic or elastomeric yarn used in systems for the production of covered elastic yarn contain much less yarn than that of the spools or cops of covering yarn. Typically, the elastic yarn on one spool is sufficient for producing a single cop of composite yarn while the covering yarn on one cop is sufficient to make several cops of composite yarn. This means that the spools of elastic yarn must be changed frequently between two subsequent covering or coating yarn cop changes. Replacement is manual. In a system generally equipped with a plurality of heads, each producing a cop of composite yarn, sensors are provided to stop head operation when the respective elastic yarn spool is finished. The operator must intervene to manually replace the ended spool of elastic yarn, and introduces the free end of the new elastic yarn in the interlacing jet to start the winding cycle of a new composite yarn cop. In the case of manual systems, the operator must also replace the completed cop with a new tube on which the new composite yarn is wound. Covering yarn output is stopped during this time.
This operative mode has considerable problems. Firstly, the downtime is long because a single operator must monitor a high number of working heads and a considerable time may elapse from the end of the spool of elastic yarn and the intervention of the operator so that the head can resume the winding cycle. Furthermore, specifically to avoid excessive machine downtime, the spools of composite yarn may be replaced before they are completely finished. The residual yarn cannot be used. This means that a not negligible quantity of elastic yarn is wasted, which is a considerable problem considering the high cost per length of this material.
On the other hand, it is not possible for the operator to arrange a spare spool of composite yarn and join the head or initial free end of the yarn on the spare spool to the tail of the yarn on the spool being processed, which would mean that the spool change would be prepared well before it ends and the entire spool would be used up. This operation is impossible because in known machines the spools of elastic yarn are not unwound by keeping them stationary, but are turned on their axis to unwind the yarn. Consequently, it is impossible for the operator to grasp the end or tail of the spool being processed and join it to the beginning of the yarn on the spare spool. This problem does not occur with the replacement of covering yarn cops because the cops are unwound without turning them on their axes. Consequently, the head-tail of the yarns wound on cops intended to be unwound in sequence can be joined to ensure continuous covering yarn feeding. Furthermore, the cops of covering yarn contain a large amount of yarn and the joining operations can be carried out after a considerable amount of time.
Covering yarn texturing devices may be arranged between the yarn feeding cop and the interlacing jet (see U.S. Pat. No. 6,393,817 and U.S. Pat. No. 5,008,992 in particular). The texturing devices comprise an oven crossed by covering yarn. This means that the yarn must be fed continuously. Indeed, stopping also only temporarily the yarn in the oven would cause destruction or unacceptable damage thereof. The covering yarn must be cut upstream of the texturing section, i.e. upstream of the oven, when the head is stopped, also only for a short time, for the operator to replace the completed elastic yarn spool. The operator re-threads the covering yarn along the entire path from the cop to the interlacing jet when the composite yarn forming head can start again after completing the operations needed to replace the spool and insert the free end of the elastic yarn in the interlacing jet. This entails a long downtime and loss of production. The problem can only be avoided if the operator is capable of intervening promptly to replace the spool of elastic yarn before the machine automatically cuts the covering yarn. Since a single operator is in charge of monitoring a high number of heads which cannot be synchronized, performing this operation in a sufficiently timely way on all heads in the system is never possible. Employment of a higher number of operators on the other hand would cause an unacceptable increase in the cost of labor.